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All productsWhich technologies go into transmitting data services over SDH networks?
1.GFD
Generic framing procedure (GFP) is a multiplexing technique defined by ITU-T G.7041. This allows mapping of client signals over an SDH network. There are two GFP modes:
| Item | GFP-F | GFP-T |
| Term | Generic Framing Procedure | Transparent Generic Framing Procedure |
| Encapsu-lation process |
GFP-F maps each variable- length client frame such as an Ethernet MAC frame into a single GFP frame. GFP-F is not used where frames are divided or reassembled. |
GFP-T allows mapping of multiple fixed-length block-coded client data streams such as ESCON, FC, and FICON into a block code for transport within a fixed-length GFP frame. |
| Difference | Variable length, large delay,non-real time | Fixed length, small delay,real time |
| Service application |
IP, PPP, Ethernet | SAN, video |
From the above info, we can see that GFP encapsulation enables the SDH network to flexibly carry various types of data services.
2.VCAT
Concatenation is an inverse multiplexing technique creating a large capacity payload container distributed over multiple smaller capacity TDM signals. There are two types of concatenation modes:
– Contiguous concatenation: Adjacent virtual containers in an STM-N frame are concatenated into one VC-4/3-Xc (X = 4, 16, 64) container.Contiguous concatenation must be enabled on all nodes that a service passes through.
– Virtual concatenation: Non-adjacent virtual containers in one or several STM-N frames are concatenated into one VC-4/3/12-Xv (X ? 64) container or VC group.Virtual concatenation can be enabled only on the source and sink nodes.
Take riding a train as an example: A family of four gets onboard only to find no four adjoining seats.
– Contiguous concatenation: We need to sit next to each other, so we need four adjoining seats.
– Virtual concatenation (VCAT): All we need is four empty seats anywhere on the train!
Let’s look at the comparisons in terms of bandwidth utilization from the different concatenation modes.
| Service | Bit Rate | Utilization without VCAT | Utilization with VCAT |
| FE | 100 Mbps | VC-4 (67%) | VC-3-2v (100%) |
| GE | 1000 Mbps | VC-4-16c (42%) | VC-4-7v (95%) |
| FC | 200 Mbps | VC-4-4c (33%) | VC-3-4v (100%) |
| FC | 1000 Mbps | VC-4-16c (42%) | VC-4-7v (95%) |
| ESCON | 200 Mbps | VC-4-4c (33%) | VC-3-4v (100%) |
Observably, VCAT enables greater efficiency and flexibility in transmitting data services over SDH networks.
3.LCAS
Both the contiguous concatenation and virtual concatenation have the following vulnerabilities:
– When any physical channel fails, all the concatenated channels fail and all services are interrupted.
– If the bandwidth is adjusted after a service is set up, the service will be adversely affected.
Link capacity adjustment scheme (LCAS) is a method to dynamically increase or decrease the bandwidth of virtual concatenated containers.The LCAS protocol is specified in ITU-T G.7042. It allows on-demand increase or decrease of the bandwidth of the virtual concatenated group in a hitless manner. This brings bandwidth on-demand capability and survivability of data traffic.