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SS7 Linksets
Group of Links between two Signalling Nodes is called Linkset.Concept of Linkset provides desired level of redundancy and load sharing between two signalling nodes.e.g. If any of sugnalling link goes down in a linkset , then all traffic can flow through other links present in that linkset.Similarly, traffic between two signalling links can be shared among all links in load sharing mode.
Few quick points to note about linkset are :
- There can be maximum 16 links in a Linkset between two Signalling Nodes
- There can be a single linkset between two signalling nodes.Though One signalling node can have multiple linksets from different adjusent signalling nodes.i.e. Signalling Node A can have linksets from Node B and Node C (or many more) but would have only single linkset between A and B as well as between A and C.
Point 1. & 2. above pose limitation of maximum 16 links between two Signalling Nodes which might not suffice ever increasing current or future requirements. e.g. 16 links between a MSC and HLR might not be able to handle increasing subscriber's signalling traffic beyond a certain limit.
Faced with this problem , following are some solutions which a Mobile Network operator has adopted :
- They use concept of Nat0 (pronounced NAT zero) and Nat1 (pronounced NAT One) to increase available links to 32 from 16. I would cover this concept in my upcoming tutorial section on MTP3.
- They migrate to HSL(High Speed Links) which allows 2 Mbps data transfer on a single link
- They upgrade to Soft Switch and substitute SIGTRAN conectivity for SS7 connectivity to lower cost and increase capacity
Classification of Links
Links can further classified as below based on type on nodes they are connecting and connection topology :
A Links(Access Links)
An A link is used to connect an SSP or SCP to STPs throughout the network.
B Links(Bridge Links)
This type of link interconnects STPs throughout a network
C Links(Cross Links)
C links used to connect a mated pair of STPs.
D Links(Diagonal Links)
D links used to connect one STP from Primary STP pair to Another STP in Secondary STP pair.There is little difference between functionality of B and D link , so these are sometimes called as B/D links.
E Links(Extended Links)
An E link is used to provide an SSP with a link to an alternate STP.
F Links(Fully Associated Links)
An F link is used to provide a direct connection between signaling endpoints. An F link can potentially be used to connect SSP to SSP,SCP to SCP or SSP to SCP.
However, F links are not normally used in networks that employ STPs.