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Mobile Transport over Packet The following topics describe Mobile Transport over Packet (MToP) services and how you can view and manage them: •
MToP Overview, page 11-1
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Circuit Emulation Overview, page 11-2
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TDM Overview, page 11-3
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IMA Overview, page 11-3
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Clocking Service Overview, page 11-4
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CEM Interfaces and Virtual CEM Interface Discovery Overview, page 11-6
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STM-N/STS-N/T3 Channelization Overview, page 11-7
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MLPPP, page 11-11
•
Synchronous Ethernet, page 11-12
MToP Overview Cisco Mobile Transport over Packet (MToP) extends Cisco IP network intelligence from the network core to the edge by preparing Radio Access Network (RAN) traffic for transport on the packet network. MToP establishes a common backbone for migration from traditional, disparate networks to a converged IP/MPLS mobile architecture. MToP uses pseudowires to extend the packet-based core closer to the edge of the network. It flattens the multiple layers of the RAN onto a single MPLS network by encapsulating and transporting time-division multiplexing (TDM), Frame Relay, and ATM traffic over MPLS. MToP builds an MPLS cloud between the distribution nodes (between access and aggregation) and the aggregation nodes on the network edge. The MPLS network is also extended over point-to-point links from the distribution nodes through Ethernet, serial, microwave, or a Layer 2 access network. The Circuit Emulation over Packet (CEoP) and STM-1c/OC-3c ATM shared port adaptors (SPAs) on aggregation Cisco 7600 Series routers terminate the pseudowire connections at the Radio Network Controller/Base Station Controller (RNC/BSC) site. CEoPS SPAs collect ATM/TDM native traffic at the distribution nodes, encapsulate them in pseudowires, and transport the traffic to the aggregation nodes using MPLS. Figure 11-1 shows an MToP network.
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Figure 11-1
MToP Network
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MToP services include: •
Using MPLS to extend the packet-based core to the edge of the network.
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Employing pseudowires, which are MPLS virtual circuit tunnels, to aggregate and transport TDM, IP, Ethernet, and ATM traffic, as well as clock synchronization, from the RAN to the network core.
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Converting RAN voice and data frames into IP packets at the cell site and transporting them over a backhaul network.
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At the central site, extracting the frames from the IP packets and rebuilding the ATM or TDM streams.
Circuit Emulation Overview Circuit emulation (CEM) provides a bridge between a TDM network and a packet network such as MPLS. The router encapsulates TDM data in MPLS packets and sends the data over a CEM pseudowire to the remote PE router. Thus, circuit emulation acts like a physical communication link across the packet network. CEM allows a virtual circuit in a packet-switching network to appear as a real, continuous-stream circuit. In packet switching, a virtual circuit has irregular delays between packets. CEM is important when a packet-switching network provides continuous stream-oriented services such as voice and video.
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TDM Overview Time division multiplexing (TDM) is a mechanism for combining two or more slower-speed data streams into a single high-speed communication channel. In this model, data from multiple sources is broken into segments that are transmitted in a defined sequence. Each incoming data stream is allocated a timeslot of a fixed length, and the data from each stream is transmitted in turn. For example, data from data stream 1 is transmitted during timeslot 1, data from data stream 2 is transmitted during timeslot 2, and so on. After each incoming stream has transmitted data, the cycle begins again with data stream 1. The transmission order is maintained so that the input streams can be reassembled at the destination. MToP encapsulates TDM streams for delivery over packet-switching networks (PSNs) using the following methods: •
Structure-Agnostic TDM over Packet (SAToP)—A method for encapsulating TDM bit-streams (T1, E1, T3, or E3) as pseudowires over PSNs.
•
Circuit Emulation Services over PSN (CESoPSN)—A method for encapsulating structured (NxDS0) TDM signals as pseudowires over PSNs.
IMA Overview Inverse Multiplexing for ATM (IMA) essentially combines the transport bandwidths of multiple links (such as T1/E1 links) in a way that collectively provides higher intermediate rates. IMA involves inverse multiplexing and demultiplexing of ATM cells in a cyclical fashion among links that are grouped to form a higher bandwidth logical link whose rate is approximately the sum of the link rates. The grouped set of links is referred to as an IMA group. Figure 11-2 illustrates IMA in one direction; the same technique applies in the opposite direction. Figure 11-2
Inverse Multiplexing and Demultiplexing of ATM Cells via IMA Groups
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IMA Virtual Link
IMA groups terminate at each end of the IMA virtual link. In the transmit direction, the ATM cell stream received from the ATM layer is distributed on a cell-by-cell basis across the multiple links within the IMA group. The receiving IMA unit recombines the cells from each link on a cell-by-cell basis, recreating the original ATM cell stream. The aggregate cell stream is then passed to the ATM layer.
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The IMA interface periodically transmits special cells containing information that permits reconstruction of the ATM cell stream at the receiving end of the IMA virtual link. The receiving end reconstructs the ATM cell stream after accounting for link differential delays, smoothing cell delay variation (CDV) introduced by the control cells, and so on. These cells, known as IMA Control Protocol (ICP) cells, define an IMA frame. The transmitter aligns the IMA frames on all links as shown in Figure 11-3, thereby allowing the receiver to adjust for differential link delays among the constituent physical links. As a result, the receiver can detect the differential delays by measuring the arrival times of the IMA frames on each link. Figure 11-3
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OC-3 Channelization
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Table 11-1 lists the channelization supported by Cisco 7600 card support. Table 11-1
Channelization T1/E1 SONET/SDH T3
Cisco 7600 Channelization
Cisco 7600 Cards •
SPA-24CHT1-CE-ATM (CEoPS SPA)
•
SPA-8XCHT1/E1
SPA-1CHOC3-CE-ATM •
SPA-4CT3/DS0
•
SPA-2CT3/DS0
Figure 11-7 shows the SONET STS-n, SDH STM-N, and TDM T3 channelization used in MToP.
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Figure 11-7
STS-N/STM-N/T3 Channelization Model
MToP Channelization Display in Cisco ANA NetworkVision MToP channelization is displayed in Cisco ANA NetworkVision by selecting the card configured for MToP channelization in the device physical inventory. Figure 11-8 shows the SONET OC-3 – STS-1 channelization on an SPA-1XCHSTM1/OC3 in Cisco ANA NetworkVision.
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Figure 11-8
SONET OC-3 – STS-1 Channelization in Cisco ANA NetworkVision
Figure 11-9 shows a four-port T3 channelization on an SPA-4XCT3/DS0 in Cisco ANA NetworkVision.
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Figure 11-9
T1 – E1 Channelization in Cisco ANA NetworkVision
For information about specific MToP channelization fields and properties, see the Cisco Active Network Abstraction 3.7.2 User Guide.
MLPPP Multilink PPP (MLPPP) is a bandwidth-on-demand protocol that can connect multiple links between two systems when needed to provide bandwidth on demand. The technique is often called bonding or link aggregation. For example, the two 64-Kbit/sec B channels of ISDN can be combined to form a single 128-Kbit/sec data channel. Another example would be to bind one or more dial-up asynchronous channels with a leased synchronous line to provide more bandwidth at peak hours of the day. MLPPP splits, recombines, and sequences datagrams across multiple logical data links. In Figure 11-10, an ATM IMA is connected to Node B. On top of the IMA, a VC is configured with a pseudowire, which requires more bandwidth between the cell router and U_PE device. To provide the bandwidth, MLPPP is configured between the cell router and the U-PE.
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MLPPP Bundle in MToP Example
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Figure 11-10
MLPPP Display in Cisco ANA NetworkVision MLPPP is displayed in Cisco ANA NetworkVision through an MLPPP Logical Inventory item shown in Figure 11-11. Each MLPPP can be expanded to display properties of the MLPPP members. In map view, MLPPP bundles are displayed as links. For more information, see the Cisco ANA 3.7 User Guide. Figure 11-11
MLPPP Logical Inventory in Cisco ANA NetworkVision
Synchronous Ethernet The ability to distribute precise frequencies around a network is known as frequency or timing synchronization. Frequency precision is required by such technologies as circuit emulation and cell-tower frequency referencing. SDH and SONET equipment provide frequency synchronization in conjunction with external timing equipment, such as Cesium oscillators and GPS, to provide precise timing synchronization across a network.
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As Ethernet equipment replaces SONET and SDH equipment, frequency synchronization becomes an Ethernet port requirement. Synchronous Ethernet (SyncE) provides the PHY-level frequency distribution of known common precision frequency references. SyncE uses a set of operations messages to maintain links. These messages ensure that a node is always deriving timing from the most reliable source, and transfer information about the quality of the timing source being used to clock the SyncE link. In SONET and SDH networks, these are known as Synchronization Status Messages (SSMs). Each timing source has a Quality Level (QL) associated with it which gives the accuracy of the clock. This QL information is transmitted across the network by SSMs over the Ethernet Synchronization Messaging Channel (ESMC), or SSMs contained in the SONET or SDH frames, so that devices know the best available source to synchronize to. To define a preferred network synchronization flow and prevent timing loops, priority values can be assigned to timing sources on each router. The combination of QL information and user-assigned priority levels allows each router to choose a timing source to clock its SyncE and SONET/SDH interfaces. SyncE services and interfaces are displayed in Cisco ANA NetworkVision under the Clock Logical Inventory item, as shown in Figure 11-12. For more information, see the Cisco ANA 3.7 User Guide. Figure 11-12
SyncE in Cisco ANA NetworkVision
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